Magnetic nano photocatalyst

Abstract

The invention discloses a magnetic nano photocatalyst, and relates to the technical field of nano functional materials and green energy, and the preparation method of the magnetic nano photocatalyst comprises the steps of magnetic substrate preparation, magnetic carrier preparation, co-doped TiO2 / graphene quantum dot precursor preparation, roasting, nitrogen plasma treatment and Ag loading. A magnetic matrix is constructed through multi-element doping of cobalt nitrate, nickel nitrate and gadolinium nitrate, the energy level of TiO2 is regulated and controlled through co-doping of thiourea and ammonium borate, oxygen vacancies are introduced into nitrogen plasma, and the performance is improved through cooperation of graphene quantum dots and Ag modification. The catalyst is high in photocatalytic activity, good in cycling stability and high in magnetic separation speed, can efficiently degrade pollutants, and has a good application prospect in the field of wastewater treatment.

Description

Technical Field

[0001] This invention relates to the fields of nanomaterials and green energy technology, and in particular to magnetic nanophotocatalysts. Background Technology

[0002] With the rapid development of industries such as dyeing and printing, and pharmaceuticals, the discharge of high-color, recalcitrant organic wastewater has surged, making it difficult for traditional biochemical methods to meet increasingly stringent emission standards. Photocatalytic oxidation technology has attracted much attention due to its mild reaction conditions and thorough mineralization. Among them, nano-photocatalysts, with their high specific surface area and strong catalytic activity, are widely used in pollutant degradation. However, traditional nano-photocatalysts (such as TiO2 and ZnO) have drawbacks such as difficulty in recovery, easy agglomeration, and narrow light response range, which limit their practical engineering applications.

[0003] To address the challenges of recycling traditional photocatalyst nanoparticles, magnetic photocatalysts have become a mainstream research area. Their core design principle involves combining magnetic components with photocatalytically active components to achieve magnetic separation and recovery. However, the preparation of traditional magnetic photocatalysts generally suffers from technical problems such as cumbersome procedures, demanding reaction conditions (e.g., high temperature and pressure), high cost, uneven dispersion, and hindered interfacial charge transfer. Furthermore, commercially available magnetic photocatalysts also exhibit various technical shortcomings, including the need for further improvement in photocatalytic efficacy, susceptibility to inhibition by complex aqueous matrices, and significant performance degradation with long-term cyclic use.

[0004] For example, invention patent CN105396591B discloses a magnetic nano-photocatalyst, its preparation method, and its application. The magnetic nano-photocatalyst has a TiO2 catalytic layer in its powder microparticles, and the catalytic layer contains an Fe3O4 magnetic core. The preparation method involves simultaneously reducing titanium salt solution and iron salt solution in a dispersing reducing solvent, followed by separation and calcination to obtain a uniformly distributed composite nano-titanium and iron catalyst. This invention's preparation method, through mild reaction conditions, composites nano-TiO2 with Fe elements, maximizing the recovery rate of the titanium dioxide photocatalyst. However, this invention still does not solve the key problems of weak interfacial bonding between the TiO2 catalytic layer and the Fe3O4 magnetic core, and hindered electron transport, resulting in poor catalyst cycle stability and a narrow light response range.

[0005] It is evident that achieving visible light response, high catalytic activity, excellent cycle stability, and convenient magnetic recovery simultaneously remains a critical technical challenge that needs to be overcome in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a magnetic nano-photocatalyst that combines highly efficient visible light photocatalytic activity, convenient magnetic separation performance, and excellent cycle stability.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a magnetic nanophotocatalyst, which is prepared by a method comprising the following steps: Step S1, Preparation of magnetic matrix: Cobalt nitrate, nickel nitrate, gadolinium nitrate, and ferric chloride are added to benzyl alcohol and ultrasonically dispersed. The mixture is then transferred to a hydrothermal reactor lined with polytetrafluoroethylene and hydrothermally reacted at 200-220℃ for 20-30 hours to obtain the hydrothermal reaction product. After cooling, the hydrothermal reaction product is centrifuged. The obtained solid is washed successively with deionized water and anhydrous ethanol and dried at 98-105℃ to constant weight to obtain magnetic powder. Finally, the magnetic powder is mixed evenly with nano-ferric oxide to obtain the magnetic matrix. Step S2, Preparation of the magnetic support: The magnetic matrix obtained in step S1 is dispersed in anhydrous ethanol and ultrasonically dispersed for 30 min to obtain a uniform suspension; deionized water and ammonia are added to the suspension, and the mixture is magnetically stirred for 10 min to adjust the pH of the system to 9-10; then, tetraethyl orthosilicate is added dropwise at a rate of 1 mL / min while stirring. After the addition is complete, the mixture is stirred at 25 °C for 3 h, and then 3-aminopropyltriethoxysilane is added and stirred at 25 °C for 3 h. After the reaction is complete, the product is separated by magnetism, washed three times each with deionized water and anhydrous ethanol, and vacuum dried at 80-90 °C for 8-10 h to obtain the magnetic support. Step S3: Preparation of co-doped TiO2 / graphene quantum dot precursor: Tetrabutyl titanate was dissolved in anhydrous ethanol and magnetically stirred for 18-22 min to obtain a titanium source solution; rare earth nitrate, thiourea, and ammonium borate were added to deionized water and stirred evenly to obtain a doped dispersion; the doped dispersion was slowly added dropwise to the titanium source solution at a dropping rate of 1 mL / min, and stirring was continued for 30 min to obtain a co-doped TiO2 precursor mixture; graphene quantum dot dispersion was slowly added dropwise to the above mixture, and stirring was continued for 35-45 min; hydrochloric acid was added to adjust the pH to 3-4, and the mixture was allowed to stand for 1.5-2.5 h to obtain a co-doped TiO2 / graphene quantum dot composite precursor sol; Step S4, Calcination: The magnetic support obtained in step S2 is added to the co-doped TiO2 / graphene quantum dot composite precursor sol prepared in step S3, and ultrasonically dispersed for 18-22 min, followed by magnetic stirring for 3-5 h; the mixture is transferred to an oven and dried at 100℃ for 10-15 h to obtain a dry gel; the dry gel is placed in a muffle furnace and calcined at 500℃ for 3-4 h in air atmosphere at a heating rate of 5℃ / min; after cooling to room temperature, it is ground through a 200-mesh sieve to obtain the primary catalyst; Step S5, Nitrogen plasma treatment: Place the nascent catalyst in a low-temperature plasma chamber, introduce N2, and treat it for 15-20 min at 100-120 W and 50-80 Pa to introduce oxygen vacancies; Step S6, Generation of magnetic nano-photocatalyst: The nascent catalyst treated with nitrogen plasma is dispersed in AgNO3 solution, irradiated with a 300W xenon lamp for 30 min, and then magnetically separated, washed, and vacuum dried in sequence to obtain the magnetic nano-photocatalyst.

[0008] Preferably, the molar ratio of cobalt nitrate, nickel nitrate, gadolinium nitrate, ferric chloride, and benzyl alcohol in step S1 is 0.2:0.2:0.1:1:(7-8).

[0009] Preferably, the mass ratio of the magnetic powder to the nano-iron oxide in step S1 is 1:(3-5); the average particle size of the nano-iron oxide is 10-80 nm.

[0010] Preferably, in step S2, the ratio of the magnetic matrix, anhydrous ethanol, deionized water, ammonia, tetraethyl orthosilicate, and 3-aminopropyltriethoxysilane is 5g:200mL:10mL:5mL:4mL:2mL; and the mass percentage concentration of the ammonia is 25%.

[0011] Preferably, in step S3, the ratio of tetrabutyl titanate, anhydrous ethanol, rare earth nitrate, thiourea, ammonium borate, deionized water, and graphene quantum dot dispersion is 20mL:80mL:0.34g:0.08g:0.06g:10mL:5.01g; and the ratio of graphene quantum dots to deionized water in the graphene quantum dot dispersion is 0.01g:5mL.

[0012] Preferably, the rare earth nitrate in step S3 is at least one of lanthanum nitrate, cerium nitrate, and gadolinium nitrate.

[0013] Preferably, the concentration of hydrochloric acid in step S3 is 0.1 mol / L.

[0014] Preferably, the ratio of the magnetic carrier and the co-doped TiO2 / graphene quantum dot composite precursor sol in step S4 is 5g:117mL.

[0015] Preferably, the flow rate of N2 in step S5 is 80 sccm.

[0016] Preferably, in step S6, the ratio of the primary catalyst after nitrogen plasma treatment to the AgNO3 solution is 0.3 g: 100 mL; and the concentration of the AgNO3 solution is 0.5 mmol·L⁻¹. -1 .

[0017] Due to the application of the above technical solution, the present invention has the following beneficial effects: (1) The magnetic nano-photocatalyst disclosed in this invention uses Co-Ni-Gd-Fe multi-metal synergistic construction of magnetic matrix, combined with precise composite of nano Fe3O4 to form multi-metal magnetic crystal synergistic effect, which not only realizes "rapid magnetic separation", but also solves the key pain points of easy oxidation of magnetic components and decrease of separation efficiency with cycle in the prior art, laying the foundation for the continuous industrial application of catalyst.

[0018] (2) The magnetic nano-photocatalyst disclosed in this invention optimizes the preparation process of the aminated SiO2 interface layer, so that the magnetic carrier and the active layer form a stable bond. Combined with the multi-component composite active layer design of rare earth-NSB multi-doping and graphene quantum dots, it achieves the synergistic effect of "accelerated interface electron transport - efficient separation of photogenerated carriers - increased catalytic active sites", which effectively improves catalytic activity and efficiency.

[0019] (3) The magnetic nano-photocatalyst disclosed in this invention introduces oxygen vacancies through nitrogen plasma treatment (100-120W, 50-80Pa), combined with Ag in-situ photoreduction modification to form Ag elemental loading. Through the dual effect of "oxygen vacancy electron capture-Ag surface plasmon resonance (SPR)," the photoresponse range is broadened to the visible light region, and the visible light utilization rate is significantly improved. The synergistic effect of this dual modification exceeds the expected effect of single modification. It not only enhances visible light absorption, but also further suppresses carrier recombination through the interfacial interaction between Ag and the active layer, enabling the catalyst to achieve efficient degradation under natural light irradiation without the need for an additional ultraviolet light source, thus greatly reducing operating costs.

[0020] (4) The magnetic nano-photocatalyst disclosed in this invention precisely optimizes the raw material ratio in each step, solving the problems of uneven dispersion and uncontrolled loading of active components in traditional preparation processes. At the same time, it adopts mild processes such as hydrothermal and sol-gel processes, avoiding oxidation or activity decay of magnetic components caused by high-temperature calcination. Compared with the high-temperature, high-pressure and complicated processes in the prior art, it not only reduces production energy consumption and cost, but also ensures the stability of product performance, achieving a "synergistic balance between high performance and large-scale production", which exceeds the traditional perception that "excellent performance requires demanding processes". Detailed Implementation

[0021] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0022] Example 1: A magnetic nanophotocatalyst, prepared by a method comprising the following steps: Step S1, Preparation of magnetic matrix: Cobalt nitrate, nickel nitrate, gadolinium nitrate, and ferric chloride were added to benzyl alcohol and ultrasonically dispersed. The mixture was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene and hydrothermally reacted at 200°C for 20 hours to obtain the hydrothermal reaction product. After cooling, the hydrothermal reaction product was centrifuged. The obtained solid was washed successively with deionized water and anhydrous ethanol and dried at 98°C to constant weight to obtain magnetic powder. Finally, the magnetic powder was mixed evenly with nano-ferric oxide to obtain the magnetic matrix. Step S2, Preparation of the magnetic support: The magnetic matrix obtained in step S1 was dispersed in anhydrous ethanol and ultrasonically dispersed for 30 min to obtain a uniform suspension; deionized water and ammonia were added to the suspension, and the mixture was magnetically stirred for 10 min to adjust the pH of the system to 9-10; then, tetraethyl orthosilicate was added while stirring at a dropping rate of 1 mL / min. After the addition was completed, the mixture was stirred at 25 °C for 3 h, and then 3-aminopropyltriethoxysilane was added and stirred at 25 °C for 3 h. After the reaction was completed, the product was separated by magnetism, washed three times each with deionized water and anhydrous ethanol, and vacuum dried at 80 °C for 8 h to obtain the magnetic support. Step S3: Preparation of co-doped TiO2 / graphene quantum dot precursor: Tetrabutyl titanate was dissolved in anhydrous ethanol and magnetically stirred for 18 min to obtain a titanium source solution; rare earth nitrate, thiourea, and ammonium borate were added to deionized water and stirred evenly to obtain a doped dispersion; the doped dispersion was slowly added dropwise to the titanium source solution at a dropping rate of 1 mL / min, and stirring was continued for 30 min to obtain a co-doped TiO2 precursor mixture; graphene quantum dot dispersion was slowly added dropwise to the above mixture, and stirring was continued for 35 min; hydrochloric acid was added to adjust the pH to 3, and the mixture was allowed to stand for 1.5 h to obtain a co-doped TiO2 / graphene quantum dot composite precursor sol; Step S4, Calcination: The magnetic support obtained in step S2 is added to the co-doped TiO2 / graphene quantum dot composite precursor sol prepared in step S3, and ultrasonically dispersed for 18 min, then magnetically stirred for 3 h; the mixture is transferred to an oven and dried at 100 °C for 10 h to obtain a dry gel; the dry gel is placed in a muffle furnace and calcined at 500 °C for 3 h in air atmosphere at a heating rate of 5 °C / min; after cooling to room temperature, it is ground through a 200-mesh sieve to obtain the primary catalyst; Step S5, Nitrogen plasma treatment: The nascent catalyst is placed in a low-temperature plasma chamber, N2 is introduced, and it is treated for 15 min at 100 W and 50 Pa to introduce oxygen vacancies. Step S6, Generation of magnetic nano-photocatalyst: The nascent catalyst treated with nitrogen plasma is dispersed in AgNO3 solution, irradiated with a 300W xenon lamp for 30 min, and then magnetically separated, washed, and vacuum dried in sequence to obtain the magnetic nano-photocatalyst.

[0023] In step S1, the molar ratio of cobalt nitrate, nickel nitrate, gadolinium nitrate, ferric chloride, and benzyl alcohol is 0.2:0.2:0.1:1:7; the mass ratio of the magnetic powder to nano-iron oxide is 1:3; and the average particle size of the nano-iron oxide is 10 nm.

[0024] In step S2, the ratio of the magnetic matrix, anhydrous ethanol, deionized water, ammonia, tetraethyl orthosilicate, and 3-aminopropyltriethoxysilane is 5g:200mL:10mL:5mL:4mL:2mL; the mass percentage concentration of the ammonia is 25%. In step S3, the ratio of the tetrabutyl titanate, anhydrous ethanol, rare earth nitrate, thiourea, ammonium borate, deionized water, and graphene quantum dot dispersion is 20mL:80mL:0.34g:0.08g:0.06g:10mL:5.01g; the ratio of graphene quantum dots to deionized water in the graphene quantum dot dispersion is 0.01g:5mL; the rare earth nitrate in step S3 is lanthanum nitrate; and the concentration of the hydrochloric acid in step S3 is 0.1mol / L.

[0025] In step S4, the ratio of the magnetic support to the co-doped TiO2 / graphene quantum dot composite precursor sol is 5 g: 117 mL; in step S5, the N2 flow rate is 80 sccm; in step S6, the ratio of the primary catalyst after nitrogen plasma treatment to AgNO3 solution is 0.3 g: 100 mL; and the concentration of the AgNO3 solution is 0.5 mmol·L⁻¹. -1 .

[0026] Example 2: A magnetic nanophotocatalyst, prepared by a method comprising the following steps: Step S1, Preparation of magnetic matrix: Cobalt nitrate, nickel nitrate, gadolinium nitrate, and ferric chloride were added to benzyl alcohol and ultrasonically dispersed. The mixture was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene and hydrothermally reacted at 205°C for 23 hours to obtain the hydrothermal reaction product. After cooling, the hydrothermal reaction product was centrifuged. The obtained solid was washed successively with deionized water and anhydrous ethanol and dried at 100°C to constant weight to obtain magnetic powder. Finally, the magnetic powder was mixed evenly with nano-ferric oxide to obtain the magnetic matrix. Step S2, Preparation of the magnetic support: The magnetic matrix obtained in step S1 was dispersed in anhydrous ethanol and ultrasonically dispersed for 30 min to obtain a uniform suspension; deionized water and ammonia were added to the suspension, and the mixture was magnetically stirred for 10 min to adjust the pH of the system to 9-10; then, tetraethyl orthosilicate was added while stirring at a dropping rate of 1 mL / min. After the addition was completed, the mixture was stirred at 25 °C for 3 h, and then 3-aminopropyltriethoxysilane was added and stirred at 25 °C for 3 h. After the reaction was completed, the product was separated by magnetism, washed three times each with deionized water and anhydrous ethanol, and vacuum dried at 83 °C for 8.5 h to obtain the magnetic support. Step S3: Preparation of co-doped TiO2 / graphene quantum dot precursor: Tetrabutyl titanate was dissolved in anhydrous ethanol and magnetically stirred for 19 min to obtain a titanium source solution; rare earth nitrate, thiourea, and ammonium borate were added to deionized water and stirred evenly to obtain a doped dispersion; the doped dispersion was slowly added dropwise to the titanium source solution at a dropping rate of 1 mL / min, and stirring was continued for 30 min to obtain a co-doped TiO2 precursor mixture; graphene quantum dot dispersion was slowly added dropwise to the above mixture, and stirring was continued for 37 min; hydrochloric acid was added to adjust the pH to 3.3, and the mixture was allowed to stand for 1.8 h to obtain a co-doped TiO2 / graphene quantum dot composite precursor sol; Step S4, Calcination: The magnetic support obtained in step S2 is added to the co-doped TiO2 / graphene quantum dot composite precursor sol prepared in step S3, and ultrasonically dispersed for 19 min, followed by magnetic stirring for 3.5 h; the mixture is transferred to an oven and dried at 100 °C for 12 h to obtain a dry gel; the dry gel is placed in a muffle furnace and calcined at 500 °C for 3.3 h in air at a heating rate of 5 °C / min; after cooling to room temperature, it is ground through a 200-mesh sieve to obtain the primary catalyst; Step S5, Nitrogen plasma treatment: The nascent catalyst is placed in a low-temperature plasma chamber, N2 is introduced, and it is treated at 105W and 60Pa for 17 minutes to introduce oxygen vacancies. Step S6, Generation of magnetic nano-photocatalyst: The nascent catalyst treated with nitrogen plasma is dispersed in AgNO3 solution, irradiated with a 300W xenon lamp for 30 min, and then magnetically separated, washed, and vacuum dried in sequence to obtain the magnetic nano-photocatalyst.

[0027] In step S1, the molar ratio of cobalt nitrate, nickel nitrate, gadolinium nitrate, ferric chloride, and benzyl alcohol is 0.2:0.2:0.1:1:7.3; the mass ratio of the magnetic powder and nano-ferric oxide is 1:3.5; the average particle size of the nano-ferric oxide is 30 nm; in step S2, the molar ratio of the magnetic matrix, anhydrous ethanol, deionized water, ammonia, tetraethyl orthosilicate, and 3-aminopropyltriethoxysilane is 5 g:200 mL:10 mL:5 mL:4 mL:2 mL; the mass percentage concentration of the ammonia is 25%.

[0028] In step S3, the ratio of tetrabutyl titanate, anhydrous ethanol, rare earth nitrate, thiourea, ammonium borate, deionized water, and graphene quantum dot dispersion is 20 mL:80 mL:0.34 g:0.08 g:0.06 g:10 mL:5.01 g; the ratio of graphene quantum dots to deionized water in the graphene quantum dot dispersion is 0.01 g:5 mL; the rare earth nitrate in step S3 is cerium nitrate; and the concentration of hydrochloric acid in step S3 is 0.1 mol / L.

[0029] In step S4, the ratio of the magnetic support to the co-doped TiO2 / graphene quantum dot composite precursor sol is 5 g: 117 mL; in step S5, the N2 flow rate is 80 sccm; in step S6, the ratio of the primary catalyst after nitrogen plasma treatment to AgNO3 solution is 0.3 g: 100 mL; and the concentration of the AgNO3 solution is 0.5 mmol·L⁻¹. -1 .

[0030] Example 3: A magnetic nanophotocatalyst, prepared by a method comprising the following steps: Step S1, Preparation of magnetic matrix: Cobalt nitrate, nickel nitrate, gadolinium nitrate and ferric chloride were added to benzyl alcohol and ultrasonically dispersed. The mixture was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene and hydrothermally reacted at 210°C for 25 hours to obtain the hydrothermal reaction product. After cooling, the hydrothermal reaction product was centrifuged. The obtained solid was washed successively with deionized water and anhydrous ethanol and dried at 102°C to constant weight to obtain magnetic powder. Finally, the magnetic powder was mixed evenly with nano-ferric oxide to obtain the magnetic matrix. Step S2, Preparation of the magnetic support: The magnetic matrix obtained in step S1 was dispersed in anhydrous ethanol and ultrasonically dispersed for 30 min to obtain a uniform suspension; deionized water and ammonia were added to the suspension, and the mixture was magnetically stirred for 10 min to adjust the pH of the system to 9-10; then, tetraethyl orthosilicate was added while stirring at a dropping rate of 1 mL / min. After the addition was completed, the mixture was stirred at 25 °C for 3 h, and then 3-aminopropyltriethoxysilane was added and stirred at 25 °C for 3 h. After the reaction was completed, the product was separated by magnetism, washed three times each with deionized water and anhydrous ethanol, and vacuum dried at 85 °C for 9 h to obtain the magnetic support. Step S3: Preparation of co-doped TiO2 / graphene quantum dot precursor: Tetrabutyl titanate was dissolved in anhydrous ethanol and magnetically stirred for 20 min to obtain a titanium source solution; rare earth nitrate, thiourea, and ammonium borate were added to deionized water and stirred evenly to obtain a doped dispersion; the doped dispersion was slowly added dropwise to the titanium source solution at a dropping rate of 1 mL / min, and stirring was continued for 30 min to obtain a co-doped TiO2 precursor mixture; graphene quantum dot dispersion was slowly added dropwise to the above mixture and stirred continuously for 40 min; hydrochloric acid was added to adjust the pH to 3.5, and the mixture was allowed to stand for 2 h to obtain a co-doped TiO2 / graphene quantum dot composite precursor sol; Step S4, Calcination: The magnetic support obtained in step S2 is added to the co-doped TiO2 / graphene quantum dot composite precursor sol prepared in step S3, and ultrasonically dispersed for 20 min, then magnetically stirred for 4 h; the mixture is transferred to an oven and dried at 100 °C for 13 h to obtain a dry gel; the dry gel is placed in a muffle furnace and calcined at 500 °C for 3.5 h in air atmosphere at a heating rate of 5 °C / min; after cooling to room temperature, it is ground through a 200-mesh sieve to obtain the primary catalyst; Step S5, Nitrogen plasma treatment: The nascent catalyst is placed in a low-temperature plasma chamber, N2 is introduced, and it is treated at 110W and 65Pa for 18 minutes to introduce oxygen vacancies. Step S6, Generation of magnetic nano-photocatalyst: The nascent catalyst treated with nitrogen plasma is dispersed in AgNO3 solution, irradiated with a 300W xenon lamp for 30 min, and then magnetically separated, washed, and vacuum dried in sequence to obtain the magnetic nano-photocatalyst.

[0031] In step S1, the molar ratio of cobalt nitrate, nickel nitrate, gadolinium nitrate, ferric chloride, and benzyl alcohol is 0.2:0.2:0.1:1:7.5; the mass ratio of the magnetic powder to nano-iron oxide is 1:4; and the average particle size of the nano-iron oxide is 50 nm.

[0032] In step S2, the ratio of the magnetic matrix, anhydrous ethanol, deionized water, ammonia, tetraethyl orthosilicate, and 3-aminopropyltriethoxysilane is 5g:200mL:10mL:5mL:4mL:2mL; the mass percentage concentration of the ammonia is 25%. In step S3, the ratio of the tetrabutyl titanate, anhydrous ethanol, rare earth nitrate, thiourea, ammonium borate, deionized water, and graphene quantum dot dispersion is 20mL:80mL:0.34g:0.08g:0.06g:10mL:5.01g; the ratio of graphene quantum dots to deionized water in the graphene quantum dot dispersion is 0.01g:5mL; the rare earth nitrate in step S3 is gadolinium nitrate; and the concentration of hydrochloric acid in step S3 is 0.1mol / L.

[0033] In step S4, the ratio of the magnetic support to the co-doped TiO2 / graphene quantum dot composite precursor sol is 5 g: 117 mL; in step S5, the N2 flow rate is 80 sccm; in step S6, the ratio of the primary catalyst after nitrogen plasma treatment to AgNO3 solution is 0.3 g: 100 mL; and the concentration of the AgNO3 solution is 0.5 mmol·L⁻¹. -1 .

[0034] Example 4: A magnetic nanophotocatalyst, prepared by a method comprising the following steps: Step S1, Preparation of magnetic matrix: Cobalt nitrate, nickel nitrate, gadolinium nitrate and ferric chloride were added to benzyl alcohol and ultrasonically dispersed. The mixture was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene and hydrothermally reacted at 215°C for 28 hours to obtain the hydrothermal reaction product. After cooling, the hydrothermal reaction product was centrifuged. The obtained solid was washed with deionized water and anhydrous ethanol in sequence and dried at 104°C to constant weight to obtain magnetic powder. Finally, the magnetic powder was mixed evenly with nano-ferric oxide to obtain the magnetic matrix. Step S2, Preparation of the magnetic support: The magnetic matrix obtained in step S1 was dispersed in anhydrous ethanol and ultrasonically dispersed for 30 min to obtain a uniform suspension; deionized water and ammonia were added to the suspension, and the mixture was magnetically stirred for 10 min to adjust the pH of the system to 9-10; then, tetraethyl orthosilicate was added while stirring at a dropping rate of 1 mL / min. After the addition was completed, the mixture was stirred at 25 °C for 3 h, and then 3-aminopropyltriethoxysilane was added and stirred at 25 °C for 3 h. After the reaction was completed, the product was separated by magnetism, washed three times each with deionized water and anhydrous ethanol, and vacuum dried at 88 °C for 9.5 h to obtain the magnetic support. Step S3: Preparation of co-doped TiO2 / graphene quantum dot precursor: Tetrabutyl titanate was dissolved in anhydrous ethanol and magnetically stirred for 21 min to obtain a titanium source solution; rare earth nitrate, thiourea, and ammonium borate were added to deionized water and stirred evenly to obtain a doped dispersion; the doped dispersion was slowly added dropwise to the titanium source solution at a dropping rate of 1 mL / min, and stirring was continued for 30 min to obtain a co-doped TiO2 precursor mixture; graphene quantum dot dispersion was slowly added dropwise to the above mixture, and stirring was continued for 43 min; hydrochloric acid was added to adjust the pH to 3.8, and the mixture was allowed to stand for 2.3 h to obtain a co-doped TiO2 / graphene quantum dot composite precursor sol; Step S4, Calcination: The magnetic support obtained in step S2 is added to the co-doped TiO2 / graphene quantum dot composite precursor sol prepared in step S3, and ultrasonically dispersed for 21 min, followed by magnetic stirring for 4.5 h; the mixture is transferred to an oven and dried at 100 °C for 14 h to obtain a dry gel; the dry gel is placed in a muffle furnace and calcined at 500 °C for 3.8 h in air at a heating rate of 5 °C / min; after cooling to room temperature, it is ground through a 200-mesh sieve to obtain the primary catalyst; Step S5, Nitrogen plasma treatment: The nascent catalyst is placed in a low-temperature plasma chamber, N2 is introduced, and it is treated at 115W and 75Pa for 19 minutes to introduce oxygen vacancies. Step S6, Generation of magnetic nano-photocatalyst: The nascent catalyst treated with nitrogen plasma is dispersed in AgNO3 solution, irradiated with a 300W xenon lamp for 30 min, and then magnetically separated, washed, and vacuum dried in sequence to obtain the magnetic nano-photocatalyst.

[0035] In step S1, the molar ratio of cobalt nitrate, nickel nitrate, gadolinium nitrate, ferric chloride, and benzyl alcohol is 0.2:0.2:0.1:1:7.8; the mass ratio of magnetic powder to nano-ferric oxide is 1:4.5; the average particle size of the nano-ferric oxide is 70 nm; in step S2, the molar ratio of magnetic matrix, anhydrous ethanol, deionized water, ammonia, tetraethyl orthosilicate, and 3-aminopropyltriethoxysilane is 5 g:200 mL:10 mL:5 mL:4 mL:2 mL; the mass percentage concentration of the ammonia is 25%.

[0036] In step S3, the mass ratio of tetrabutyl titanate, anhydrous ethanol, rare earth nitrate, thiourea, ammonium borate, deionized water, and graphene quantum dot dispersion is 20 mL:80 mL:0.34 g:0.08 g:0.06 g:10 mL:5.01 g; the mass ratio of graphene quantum dots to deionized water in the graphene quantum dot dispersion is 0.01 g:5 mL; the rare earth nitrate in step S3 is a mixture of lanthanum nitrate, cerium nitrate, and gadolinium nitrate in a mass ratio of 1:2:1; and the concentration of hydrochloric acid in step S3 is 0.1 mol / L.

[0037] In step S4, the ratio of the magnetic support to the co-doped TiO2 / graphene quantum dot composite precursor sol is 5 g: 117 mL; in step S5, the N2 flow rate is 80 sccm; in step S6, the ratio of the primary catalyst after nitrogen plasma treatment to AgNO3 solution is 0.3 g: 100 mL; and the concentration of the AgNO3 solution is 0.5 mmol·L⁻¹. -1 .

[0038] Example 5: A magnetic nanophotocatalyst, prepared by a method comprising the following steps: Step S1, Preparation of magnetic matrix: Cobalt nitrate, nickel nitrate, gadolinium nitrate and ferric chloride were added to benzyl alcohol and ultrasonically dispersed. The mixture was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene and hydrothermally reacted at 220°C for 30 hours to obtain the hydrothermal reaction product. After cooling, the hydrothermal reaction product was centrifuged. The obtained solid was washed with deionized water and anhydrous ethanol in sequence and dried at 105°C to constant weight to obtain magnetic powder. Finally, the magnetic powder was mixed evenly with nano-ferric oxide to obtain the magnetic matrix. Step S2, Preparation of the magnetic support: The magnetic matrix obtained in step S1 was dispersed in anhydrous ethanol and ultrasonically dispersed for 30 min to obtain a uniform suspension; deionized water and ammonia were added to the suspension, and the mixture was magnetically stirred for 10 min to adjust the pH of the system to 9-10; then, tetraethyl orthosilicate was added while stirring at a dropping rate of 1 mL / min. After the addition was completed, the mixture was stirred at 25 °C for 3 h, and then 3-aminopropyltriethoxysilane was added and stirred at 25 °C for 3 h. After the reaction was completed, the product was separated by magnetism, washed three times each with deionized water and anhydrous ethanol, and dried under vacuum at 90 °C for 10 h to obtain the magnetic support. Step S3: Preparation of co-doped TiO2 / graphene quantum dot precursor: Tetrabutyl titanate was dissolved in anhydrous ethanol and magnetically stirred for 22 min to obtain a titanium source solution; rare earth nitrate, thiourea, and ammonium borate were added to deionized water and stirred evenly to obtain a doped dispersion; the doped dispersion was slowly added dropwise to the titanium source solution at a dropping rate of 1 mL / min, and stirring was continued for 30 min to obtain a co-doped TiO2 precursor mixture; graphene quantum dot dispersion was slowly added dropwise to the above mixture, and stirring was continued for 45 min; hydrochloric acid was added to adjust the pH to 4, and the mixture was allowed to stand for 2.5 h to obtain a co-doped TiO2 / graphene quantum dot composite precursor sol; Step S4, Calcination: The magnetic support obtained in step S2 is added to the co-doped TiO2 / graphene quantum dot composite precursor sol prepared in step S3, and ultrasonically dispersed for 22 min, then magnetically stirred for 5 h; the mixture is transferred to an oven and dried at 100 °C for 15 h to obtain a dry gel; the dry gel is placed in a muffle furnace and calcined at 500 °C for 4 h in air atmosphere at a heating rate of 5 °C / min; after cooling to room temperature, it is ground through a 200-mesh sieve to obtain the primary catalyst; Step S5, Nitrogen plasma treatment: The nascent catalyst is placed in a low-temperature plasma chamber, N2 is introduced, and it is treated at 120W and 80Pa for 20 minutes to introduce oxygen vacancies. Step S6, Generation of magnetic nano-photocatalyst: The nascent catalyst treated with nitrogen plasma is dispersed in AgNO3 solution, irradiated with a 300W xenon lamp for 30 min, and then magnetically separated, washed, and vacuum dried in sequence to obtain the magnetic nano-photocatalyst.

[0039] In step S1, the molar ratio of cobalt nitrate, nickel nitrate, gadolinium nitrate, ferric chloride, and benzyl alcohol is 0.2:0.2:0.1:1:8; the mass ratio of the magnetic powder and nano-ferric oxide is 1:5; the average particle size of the nano-ferric oxide is 80 nm; in step S2, the molar ratio of the magnetic matrix, anhydrous ethanol, deionized water, ammonia, tetraethyl orthosilicate, and 3-aminopropyltriethoxysilane is 5 g:200 mL:10 mL:5 mL:4 mL:2 mL; the mass percentage of the ammonia is... The concentration is 25%; the ratio of tetrabutyl titanate, anhydrous ethanol, rare earth nitrate, thiourea, ammonium borate, deionized water, and graphene quantum dot dispersion in step S3 is 20mL:80mL:0.34g:0.08g:0.06g:10mL:5.01g; the ratio of graphene quantum dots to deionized water in the graphene quantum dot dispersion is 0.01g:5mL; the rare earth nitrate in step S3 is lanthanum nitrate; the concentration of hydrochloric acid in step S3 is 0.1mol / L.

[0040] In step S4, the ratio of the magnetic support to the co-doped TiO2 / graphene quantum dot composite precursor sol is 5 g: 117 mL; in step S5, the N2 flow rate is 80 sccm; in step S6, the ratio of the primary catalyst after nitrogen plasma treatment to AgNO3 solution is 0.3 g: 100 mL; and the concentration of the AgNO3 solution is 0.5 mmol·L⁻¹. -1 .

[0041] Comparative Example 1 A magnetic nanophotocatalyst, which is basically the same as that in Example 5, except that gadolinium nitrate is not added in step S1.

[0042] Comparative Example 2 A magnetic nanophotocatalyst is basically the same as that in Example 5, except that in step S3, an equal amount of thiourea is used instead of ammonium borate.

[0043] Comparative Example 3 A magnetic nanophotocatalyst is basically the same as that in Example 5, except that in step S3, an equal amount of ammonium borate is used instead of thiourea.

[0044] Comparative Example 4 A magnetic nanophotocatalyst, which is basically the same as that in Example 5, except that it does not have a nitrogen plasma treatment step.

[0045] To further illustrate the beneficial technical effects of the various embodiments of the present invention, relevant performance tests were conducted on the magnetic nano-photocatalysts prepared in Example 5 and Comparative Examples 1-4. The test results are shown in Table 1, and the test methods are as follows: (1) Photocatalytic activity test: Using methylene blue as the target pollutant, 500 mL of methylene blue solution with an initial concentration of 10 μmol / L was prepared; 0.2 g of photocatalyst was added to the solution, and the mixture was magnetically stirred for 30 min in the dark to reach adsorption-desorption equilibrium; a xenon lamp was used as a simulated solar light source (wavelength 320-780 nm, radiation intensity 100 mW / cm²). 2 The photocatalytic reaction was initiated. Every 20 minutes, 5 mL of the reaction solution was taken, filtered through a 0.22 μm filter membrane, and the absorbance was measured at a wavelength of 664 nm using a UV-Vis spectrophotometer to calculate the methylene blue degradation rate.

[0046] (2) Cyclic stability test: Repeat the above photocatalytic activity test procedure. After each reaction, the catalyst is separated by a magnet, washed with deionized water 3 times, dried at 60°C and then carried out the next cycle. A total of 5 cycles are carried out, and the methylene blue degradation rate is calculated after 5 cycles.

[0047] (3) Magnetic separation efficiency test: Weigh 50.0 mg of the magnetic nano-photocatalyst to be tested, place it in a 100 mL glass graduated cylinder, add 100 mL of deionized water, and seal the bottle tightly; place the graduated cylinder in an ultrasonic cleaner and ultrasonically disperse for 10 minutes to ensure that the catalyst particles are fully and uniformly dispersed in the water, and that no visible agglomerates settle to the bottom; after ultrasonication, immediately use a magnetic stirrer to stir for 10 seconds to simulate the initial suspension state of the catalyst in the wastewater to be treated. Start the stopwatch and simultaneously place a magnet with a magnetic field strength of 0.5T firmly against the lower middle part of the outer wall of the graduated cylinder (below the liquid surface), keeping the magnet in a fixed position. Visually observe the changes in the suspension in the graduated cylinder. The catalyst particles will be attracted to the tube wall on the side where the magnet is located under the action of the magnetic field and slide down and accumulate. When the main part of the suspension (supernatant) becomes clear and transparent, and when a laser pointer is used to illuminate the graduated cylinder horizontally from one side, no obvious Tyndall effect light path can be observed on the other side (i.e., no obvious scattering of light by suspended particles), the magnetic separation is considered to be complete. Immediately stop the stopwatch and record the time taken. This time is the "magnetic separation time" of this test.

[0048] Table 1 Performance Test Results

[0049] As shown in Table 1, the overall performance of the magnetic nano-photocatalyst prepared in Example 5 of this invention is significantly better than that of the comparative examples: In terms of photocatalytic activity, the methylene blue degradation rate of Example 5 in 60 min is as high as 99.6%, which is much higher than that of Comparative Example 1 (92.3%), Comparative Example 2 (88.7%), Comparative Example 3 (89.1%) and Comparative Example 4 (90.5%); In terms of cycle stability, the degradation rate of Example 5 remains at 98.2% after 5 cycles, which is significantly better than that of the comparative examples (85.6%, 79.3%, 80.2% and 82.4%); In terms of magnetic separation performance, the magnetic separation time of Example 5 is only 10 s, which is much shorter than that of Comparative Example 1 (25 s), Comparative Example 2 (16 s), Comparative Example 3 (17 s) and Comparative Example 4 (13 s). The above data fully demonstrates that the present invention, through the synergistic effect of key technical features such as gadolinium nitrate doping to construct a multi-element magnetic matrix, co-doping of thiourea and ammonium borate to regulate the TiO2 energy level structure, and nitrogen plasma treatment to introduce oxygen vacancies, has successfully achieved a synergistic improvement in the photocatalytic activity, cycle stability, and magnetic separation performance of magnetic nanophotocatalysts, and has excellent practical application value.

[0050] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A magnetic nanophotocatalyst, characterized in that, It is prepared by a method including the following steps: Step S1, Preparation of magnetic matrix: Cobalt nitrate, nickel nitrate, gadolinium nitrate, and ferric chloride are added to benzyl alcohol and ultrasonically dispersed. The mixture is then transferred to a hydrothermal reactor lined with polytetrafluoroethylene and hydrothermally reacted at 200-220℃ for 20-30 hours to obtain the hydrothermal reaction product. After cooling, the hydrothermal reaction product is centrifuged. The obtained solid is washed successively with deionized water and anhydrous ethanol and dried at 98-105℃ to constant weight to obtain magnetic powder. Finally, the magnetic powder is mixed evenly with nano-ferric oxide to obtain the magnetic matrix. Step S2, Preparation of the magnetic support: The magnetic matrix obtained in step S1 is dispersed in anhydrous ethanol and ultrasonically dispersed for 30 min to obtain a uniform suspension; deionized water and ammonia are added to the suspension, and the mixture is magnetically stirred for 10 min to adjust the pH of the system to 9-10; then, tetraethyl orthosilicate is added dropwise at a rate of 1 mL / min while stirring. After the addition is complete, the mixture is stirred at 25 °C for 3 h, and then 3-aminopropyltriethoxysilane is added and stirred at 25 °C for 3 h. After the reaction is complete, the product is separated by magnetism, washed three times each with deionized water and anhydrous ethanol, and vacuum dried at 80-90 °C for 8-10 h to obtain the magnetic support. Step S3, Preparation of co-doped TiO2 / graphene quantum dot precursor: Tetrabutyl titanate was dissolved in anhydrous ethanol and magnetically stirred for 18-22 min to obtain a titanium source solution; rare earth nitrate, thiourea, and ammonium borate were added to deionized water and stirred evenly to obtain a doped dispersion system; The doped dispersion was slowly added dropwise to the titanium source solution at a rate of 1 mL / min, and stirring was continued for 30 min to obtain a co-doped TiO2 precursor mixture. Separately, a graphene quantum dot dispersion was slowly added dropwise to the above mixture, and stirring was continued for 35-45 min. Hydrochloric acid was added to adjust the pH to 3-4, and the mixture was allowed to stand for 1.5-2.5 h to obtain a co-doped TiO2 / graphene quantum dot composite precursor sol. Step S4, Calcination: The magnetic support obtained in step S2 is added to the co-doped TiO2 / graphene quantum dot composite precursor sol prepared in step S3, and ultrasonically dispersed for 18-22 min, followed by magnetic stirring for 3-5 h; the mixture is transferred to an oven and dried at 100℃ for 10-15 h to obtain a dry gel; the dry gel is placed in a muffle furnace and calcined at 500℃ for 3-4 h in air atmosphere at a heating rate of 5℃ / min; after cooling to room temperature, it is ground through a 200-mesh sieve to obtain the primary catalyst; Step S5, Nitrogen plasma treatment: Place the nascent catalyst in a low-temperature plasma chamber, introduce N2, and treat it for 15-20 min at 100-120 W and 50-80 Pa to introduce oxygen vacancies; Step S6, Generation of magnetic nano-photocatalyst: The nascent catalyst treated with nitrogen plasma is dispersed in AgNO3 solution, irradiated with a 300W xenon lamp for 30 min, and then magnetically separated, washed, and vacuum dried in sequence to obtain the magnetic nano-photocatalyst.

2. The magnetic nanophotocatalyst according to claim 1, characterized in that, The molar ratio of cobalt nitrate, nickel nitrate, gadolinium nitrate, ferric chloride, and benzyl alcohol in step S1 is 0.2:0.2:0.1:1:(7-8).

3. The magnetic nanophotocatalyst according to claim 1, characterized in that, The mass ratio of the magnetic powder and nano-iron oxide in step S1 is 1:(3-5); the average particle size of the nano-iron oxide is 10-80 nm.

4. The magnetic nanophotocatalyst according to claim 1, characterized in that, In step S2, the ratio of the magnetic matrix, anhydrous ethanol, deionized water, ammonia, tetraethyl orthosilicate, and 3-aminopropyltriethoxysilane is 5g:200mL:10mL:5mL:4mL:2mL; and the mass percentage concentration of the ammonia is 25%.

5. The magnetic nanophotocatalyst according to claim 1, characterized in that, In step S3, the ratio of tetrabutyl titanate, anhydrous ethanol, rare earth nitrate, thiourea, ammonium borate, deionized water, and graphene quantum dot dispersion is 20 mL:80 mL:0.34 g:0.08 g:0.06 g:10 mL:5.01 g; and the ratio of graphene quantum dots to deionized water in the graphene quantum dot dispersion is 0.01 g:5 mL.

6. The magnetic nanophotocatalyst according to claim 1, characterized in that, The rare earth nitrate mentioned in step S3 is at least one of lanthanum nitrate, cerium nitrate, and gadolinium nitrate; the concentration of hydrochloric acid mentioned in step S3 is 0.1 mol / L.

7. The magnetic nanophotocatalyst according to claim 1, characterized in that, The ratio of the magnetic carrier and the co-doped TiO2 / graphene quantum dot composite precursor sol in step S4 is 5g:117mL.

8. The magnetic nanophotocatalyst according to claim 1, characterized in that, The flow rate of N2 in step S5 is 80 sccm.

9. The magnetic nanophotocatalyst according to claim 1, characterized in that, In step S6, the ratio of the primary catalyst after nitrogen plasma treatment to the AgNO3 solution is 0.3 g: 100 mL.

10. The magnetic nanophotocatalyst according to claim 1, characterized in that, The concentration of the AgNO3 solution was 0.5 mmol·L⁻¹. -1 .

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